Interaction of 14-3-3 proteins with their targets depends not only on the phosphorylation status of the target but also on that of 14-3-3 (Fu et al., 2000). In this work we demonstrated that the maize 14-3-3 isoform GF14-6 is a substrate of the tyrosine kinase insulin growth factor receptor 1. By means of site-directed mutants of GF14-6, we identified Tyr-137 as the specific tyrosine residue phosphorylated by the insulin growth factor receptor 1. Phosphorylation of GF14-6 on Tyr-137 lowered its affinity for a peptide mimicking the 14-3-3 binding site of the plant plasma membrane H+-ATPase. Moreover, phosphorylation in planta of 14-3-3 tyrosine residues, resulting from incubation with the tyrosine phosphatase inhibitor, phenylarsine oxide, decreased their association to the H+-ATPase.